There is nothing new about crossing racial boundaries; what is new is the frequency of border crossings and boundary hoppings and the refusal to bow to the thorn-filled American concept, perhaps unknown outside the United States, that each person has a race but only one. Racial blending is undermining the master idea that race is an irreducible marker among diverse peoples—an idea in any case that always has been socially constructed and has no scientific validity. (In this century, revivals of purportedly scientifically provable racial categories have surfaced every generation or so. Ideas die hard, especially when they are socially and politically useful.) Twenty-five years ago, it would have been unthinkable for Time-Life to publish a computer-created chart of racial synthesizing; seventy-five years ago, an issue on “The New Face of America” might have put Time out of business for promoting racial impurity.

As scientists explore the human genome and medicines tailored to particular genes, a provocative question emerges about whether there is a genetic marker that could explain why some treatments work better for different racial groups. And some say the narrow focus on race misses the point of social disparities and what we now know about genetics. (00:54:12)

(Interview suspends at 00:26:40 for a short news update, then restarts at 00:30:23.)